These studies are directed at the detailed immunochemical characterization of a number of gonococcal surface antigens known or presumed to be important in the pathogenesis of gonococcal infection. Pili mediate specific adherence to human cells. We propose to identify and characterize the human cell receptor which interacts with pili. Inasmuch as gonococcal pili in our hands are powerful hemagglutinators, we will isolate the receptor from human red cells. We will determine whether the receptor is a protein, a glycoprotein, or a glycolipid. The immunochemistry of two classes of outer membrane proteins, the serotype proteins, and the "opacity" proteins will be investigated in detail. We will attempt to determine the covalent structure of a representative major outer membrane protein and relate this to peptide mapping of all gonococcal serotype proteins. The extracellular enzyme IgAl protease will be isolated and its immunogenicity determined. We will determine whether antibodies to the enzyme are directed at the active site and are inactivating. A representative number of strains will be screened to determine whether serological variants of this enzyme exist or whether it is produced as a proenzyme.